The invention is in the field of article and workpiece handling, and more specifically in the field of article and workpiece inspection and identification.
It is often desirable to identify articles and workpieces by punch-stamping or engraving markings into the article and workpiece, or by otherwise affixing markings thereto. For example, when handguns are manufactured serial numbers are punch-stamped or engraved on several different metal parts at the time the parts are made. In the process of assembling the parts into a handgun it may be desirable (perhaps even required) to record the serial numbers of the various components and the serial number of the assembled handgun. This is typically done at present by manually reading each serial number, which is time consuming and prone to error, partly because of the unavoidable fatigue from repetitive work. As another example, when fuel rods for nuclear reactors are handled, it is typically required to keep careful records of the stamped or engraved serial numbers of the rods. This may necessitate frequent manual reading of such serial numbers, with the associated difficulties of safely handling the nuclear material. Similarly, in other assembling operations it may be desirable to keep track of various markings that have been punch-stamped, engraved or otherwise formed on workpieces.
While some markings can be detected and identified by a machine, for example by mechanical or electrical brushes or by prior art character recognition machines, this is not always practicable or possible. For example, if markings are to be detected and identified by mechanical or electrical brushes, the markings must have special characteristics which in many cases may not be practicable to implement. In the example of serial numbers punch-stamped or engraved into metal parts, it is typically not possible to read the markings by such electrical or mechanical brushes with acceptable accuracy because of the relatively small size of the markings and because of the relatively low contrast between the background and the marking. In some cases character recognition machines of the type used to read printed material may be used to read markings on workpieces, but such machines require special type fonts and clear contrast between the marking and the background. Therefore, while such machines may be used in certain situations, such as when detecting and identifying certain special types of printed labels and the like, they are not useful in the typical industrial situation, where markings such as serial numbers are punch-stamped or engraved into workpieces or the workpieces are provided with other markings which are not uniform or well defined and which are on a low contrast background. In one prior art example (U.S. Pat. No. 3,810,159) raised markings on tires are read by a machine, but only by either heating or cooling the tire so as to get differential infrared radiation as between the marking and the background. For such reasons, it has not been possible in the prior art to satisfactorily detect and identify low contrast markings of the type typically used in an industrial environment despite the need to do so in order to increase the control over a given manufacturing or assembly processes and in order to reduce labor costs.